The present invention relates to upgrading thermal black reject material to produce a low grit carbon black.
In the manufacture of carbon black, grit frequently becomes concentrated in the +10 mesh material. To produce a low grit black it frequently becomes necessary to reduce grit levels by removing the 10+ mesh material by a screening method. This is effective in reducing grit levels but it also removes large pellets of low grit material. Micropulverizing this material does not reduce grit levels significantly. It may reduce 35 mesh grit but increases 60 and 325 mesh grit at the same time.
In prior art processes, a carbon black is produced by thermal decomposition of a hydrocarbon feedstock, the carbon black is pelletized, the over-sized material removed from the carbon black by a screening method and the over-sized material is sucked by a vacuum into a bag filter where it is impinged on a plate. The preferred means of pelletizing thermal carbon black is in a drum roller. The preferred screening means is a rotating screen which removes the 10+ mesh material.
A prior art solution to the grit problem is to separate the gritty material from the carbon black prior to pelletization. This process reduced the gritty material in the product, but it also caused large amounts of low grit material to be classified as reject material.